Service/mirrors

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Introduction

A content delivery network or Content Delivery Network (CDN) is a system of computers containing copies of data, placed at various points in a network so as to maximize bandwidth for access to the data from clients throughout the network. A client accesses a copy of the data near to the client, as opposed to all clients accessing the same central server, thereby causing a bottleneck near that server.

Goals

  • Reduce bandwidth at primary download server.
  • Improve quality of service for users.
  • Move content closer to users, thus reducing latency.

Architecture

The Sugar Labs Content Delivery Network uses MirrorBrain as a redirector. The redirector, which lives in a Sugar Labs data center, keeps track of which files are available on which mirror. When a user requests a file, the redirector points the user to the correct mirror and automatically starts the file download.

Mirrors

The current list of available mirrors is available at http://mirrors.sugarlabs.org/

Considerations

Bandwidth

To run a mirror you need a lot of bandwidth! You should look at the total bandwidth used by all the mirrors.

If you have trouble with bandwidth, you should look at CloudFlare.

HDD Space

Hosting a mirror takes a lot of space. If you don't have a lot of space you can only choose to mirror some parts. For example exclude all directories but the activities (~13gb):

 rsync -avzh rsync://download.sugarlabs.org/pub --exclude 'dextrose' --exclude 'hexoquinasa' --exclude 'images' --exclude 'sources' --exclude 'docs' --exclude 'packages' --exclude 'soas' /rsync/download.sugarlabs.org

Setting up a new mirror

For mirror administrators

All you need is a web server with enough bandwidth to serve the files. To set up a new mirror, the site administrator needs to:

  • First lets make a directory to store the data:
 mkdir /rsync
 mkdir /rsync/download.sugarlabs.org
  • Then lets use rsync to download the data (warning: takes a long time)
 rsync -avzh rsync://download.sugarlabs.org/pub /rsync/download.sugarlabs.org
  • Save the rsync command as a shell script and make it executable:
 echo "rsync -avzh rsync://download.sugarlabs.org/pub /rsync/download.sugarlabs.org" > /rsync/download.sugarlabs.org/sync.sh
 chmod 774 /rsync/download.sugarlabs.org/sync.sh
  • Then lets make this to sync automatically. We can use a cron job to do that. You could make sync every 2 hours:
 echo "0 */2 * * * /rsync/download.sugarlabs.org/sync.sh" > asloSyncCronJob.txt
 crontab asloSyncCronJob.txt

If you don't want it to sync every 2 hours, have a look at a cron tutorial to change that value.

  • Publish the files via HTTP. Look at your http server documentation on how to do that. You could set up a virtual host to serve these files: in nginx in apache
  • Setup a rsync mirror so we can view the status of your mirror. To do so, create a rsyncd.conf file and open it:
 sudo nano rsyncd.conf

Then insert the following config:

 log file = /rsync/log
 [sugarlabs]
     path = /rsync/download.sugarlabs.org
     comment = PUT SOME INFORMATION HERE - LIKE A MOTD
     read only = true
     list = yes

Save and quit nano. Then start rsyncd so it can serve your files:

 rsync --daemon --config=/etc/rsyncd.conf
  • Alert the Sugar Labs System Administrators that they would like their mirror into rotation, including the following information in the request:
    • Name and URL of the mirror operator (e.g. organization)
    • Name and email address of the administrative contact
    • ISO 3166-1 alpha-2 country code of the server location
    • HTTP base URL of the files on the mirror (typically http://mirrors.example.org/sugarlabs/)
    • rsync base URL of the files on the mirror (typically rsync://mirrors.example.org/sugarlabs/)

Please contact sysadmin AT sugarlabs DOT org if you are interested in hosting a mirror.

For Sugar Labs sysadmins

To add a new mirror to the MirrorBrain redirector:

  • Choose a name for the mirror, usually the host name.
  • Register the mirror with MirrorBrain:
sudo -u mirrorbrain mb new <mirror name> --operator-name <operator name> \
 --operator-url <operator URL> -a <admin name> -e <admin email> \
 -c <country code> -H <base HTTP URL> -R <base rsync URL> -F <base FTP URL>
  • Scan and enable the mirror:
sudo -u mirrorbrain mb scan -e <mirror name>
  • Export the list of mirrors for mirmon (a hourly cronjob does this, but if you don't want to wait...):
mb export --format=mirmon-apache | sudo -u mirrorbrain tee /srv/mirrorbrain/mirmon/mirrorlist-export
  • Finally, re-run mirmon to ensure it can check the health of the mirror (this is also done by a cronjob, but our patience is very short):
sudo -u mirrorbrain mirmon -v -get all -c /etc/mirmon.conf